Diamond led devices and associated methods

ABSTRACT

LED devices incorporating diamond materials and methods for making such devices are provided. One such method may include forming epitaxially a substantially single crystal SiC layer on a substantially single crystal Si wafer, forming epitaxially a substantially single crystal diamond layer on the SiC layer, doping the diamond layer to form a conductive diamond layer, removing the Si wafer to expose the SiC layer opposite to the conductive diamond layer, forming epitaxially a plurality of semiconductor layers on the SiC layer such that at least one of the semiconductive layers contacts the SiC layer, and coupling an n-type electrode to at least one of the semiconductor layers such that the plurality of semiconductor layers is functionally located between the conductive diamond layer and the n-type electrode.

PRIORITY DATA

This application is a divisional of U.S. patent application Ser. No.12/755,034, filed on Apr. 6, 2010, which is a continuation-in-part ofU.S. patent application Ser. No. 12/686,288, filed on Jan. 12, 2010,which is a divisional of U.S. patent application Ser. No. 11/809,720,filed on May 31, 2007, now issued as U.S. Pat. No. 7,646,025, each ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor devices andassociated methods. Accordingly, the present invention involves theelectrical and material science fields.

BACKGROUND OF THE INVENTION

In many developed countries, major portions of the populations considerelectronic devices to be integral to their lives. Such increasing useand dependence has generated a demand for electronics devices that aresmaller and faster. As electronic circuitry increases in speed anddecreases in size, cooling of such devices becomes problematic.

Electronic devices generally contain printed circuit boards havingintegrally connected electronic components that allow the overallfunctionality of the device. These electronic components, such asprocessors, transistors, resistors, capacitors, light-emitting diodes(LEDs), etc., generate significant amounts of heat. As it builds, heatcan cause various thermal problems associated with such electroniccomponents. Significant amounts of heat can affect the reliability of anelectronic device, or even cause it to fail by, for example, causingburn out or shorting both within the electronic components themselvesand across the surface of the printed circuit board. Thus, the buildupof heat can ultimately affect the functional life of the electronicdevice. This is particularly problematic for electronic components withhigh power and high current demands, as well as for the printed circuitboards that support them.

Various cooling devices have been employed such as fans, heat sinks,Peltier and liquid cooling devices, etc., as means of reducing heatbuildup in electronic devices. As increased speed and power consumptioncause increasing heat buildup, such cooling devices generally mustincrease in size to be effective and may also require power to operate.For example, fans must be increased in size and speed to increaseairflow, and heat sinks must be increased in size to increase heatcapacity and surface area. The demand for smaller electronic devices,however, not only precludes increasing the size of such cooling devices,but may also require a significant size decrease.

As a result, methods and associated devices are being sought to provideadequate cooling of electronic devices while minimizing size and powerconstraints placed on such devices due to cooling.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides semiconductor devices havingimproved thermal properties and methods for making such devices. In oneaspect, for example, an LED device is provided having a conductivediamond layer, a SiC layer coupled to the diamond layer, a plurality ofsemiconductor layers, at least one of which is coupled to the SiC layer,and an n-type electrode coupled to at least one of the plurality ofsemiconductor layers, where the conductive diamond layer and the n-typeelectrode are arranged such that there is a substantially linearconductive pathway therebetween. Although numerous configurations forsemiconductor layers are contemplated, in one aspect the plurality ofsemiconductor layers is arranged in series between the conductivediamond layer and the n-type electrode. Depending on the varioustechniques used to deposit a material, the crystal lattice of the SiClayer may be epitaxially coupled or matched to the crystal lattice ofthe conductive diamond layer. Additionally, the crystal lattice of theSiC layer may be epitaxially coupled or matched to the crystal latticeof at least one of the semiconductor layers.

Numerous semiconductor materials may be utilized in the construction ofsuch a semiconductor device, depending on the intended application ofthe device. For example, in one aspect the semiconductor material mayinclude at least one of silicon germanium, gallium arsenide, galliumnitride, germanium, zinc sulfide, gallium phosphide, gallium antimonide,gallium indium arsenide phosphide, aluminum phosphide, aluminumarsenide, aluminum gallium arsenide, gallium nitride, boron nitride,aluminum nitride, indium arsenide, indium phosphide, indium antimonide,indium nitride, and combinations thereof.

In another aspect, the semiconductor material may include at least oneof gallium nitride, boron nitride, aluminum nitride, indium nitride, andcombinations thereof. In a more specific aspect, the semiconductormaterial may include gallium nitride. In another more specific aspect,the semiconductor material may include aluminum nitride.

The conductive diamond layers according to aspects of the presentinvention may vary widely depending on the intended application of thedevice. For example, in one aspect the conductive diamond layer may be asingle crystal or substantially a single crystal. In another aspect, theconductive diamond layer may be a conductive adynamic diamond layer.Additionally, in some applications it may be beneficial for theconductive diamond layer to be substantially transparent.

Various techniques may be employed to render a diamond layer conductive.For example, various impurities may be doped into the crystal lattice ofthe diamond layer. Such impurities may include elements such as Si, B,P, N, Li, Al, Ga, etc. In one specific aspect, for example, the diamondlayer may be doped with B. Impurities may also include metallicparticles within the crystal lattice, provided they do not interferewith the function of the device, such as by blocking light emitted froman LED.

The present invention additionally provides methods for making LEDdevices. In one aspect such a method may include forming epitaxially asubstantially single crystal SiC layer on a substantially single crystalSi wafer, forming epitaxially a substantially single crystal diamondlayer on the SiC layer, doping the diamond layer to form a conductivediamond layer, removing the Si wafer to expose the SiC layer opposite tothe conductive diamond layer, forming epitaxially a plurality ofsemiconductor layers on the SiC layer such that at least one of thesemiconductive layers contacts the SiC layer, and coupling an n-typeelectrode to at least one of the semiconductor layers such that theplurality of semiconductor layers is functionally located between theconductive diamond layer and the n-type electrode.

Various techniques may be utilized for the epitaxial deposition of thediamond layer on the SiC layer. For example, in one aspect forming anepitaxial diamond layer may further include grading a growth surface ofthe Si wafer from Si to SiC to form the SiC layer, and grading a growthsurface of the SiC layer from SiC to diamond to form the diamond layer.In another aspect, forming an epitaxial layer of single crystal SiC mayfurther include forming a conformal amorphous diamond layer on a singlecrystal Si wafer to form the SiC layer in situ therebetween, removingthe conformal amorphous diamond layer to expose the SiC layer. Followingremoval of the conformal amorphous diamond layer the conductive diamondlayer may be formed on the exposed SiC layer.

The present invention also provides LED devices having a conductivediamond substrate, a substantially single crystal SiC layer coupled tothe diamond substrate, a plurality of semiconductor layers epitaxiallycoupled to the SiC layer, and an n-type electrode coupled to at leastone of the semiconductor layers, such that the plurality ofsemiconductor layers is functionally located between the conductivediamond layer and the n-type electrode.

There has thus been outlined, rather broadly, various features of theinvention so that the detailed description thereof that follows may bebetter understood, and so that the present contribution to the art maybe better appreciated. Other features of the present invention willbecome clearer from the following detailed description of the invention,taken with the accompanying claims, or may be learned by the practice ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view of an LED device being constructed inaccordance with one embodiment of the present invention.

FIG. 2 is a cross-section view of an LED device in accordance with oneembodiment of the present invention.

FIG. 3 is a cross-section view of selected steps in the formation of anLED device in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Definitions

In describing and claiming the present invention, the followingterminology will be used in accordance with the definitions set forthbelow.

The singular forms “a,” “an,” and, “the” include plural referents unlessthe context clearly dictates otherwise. Thus, for example, reference to“a heat source” includes reference to one or more of such sources, andreference to “the diamond layer” includes reference to one or more ofsuch layers.

The terms “heat transfer,” “heat movement,” and “heat transmission” canbe used interchangeably, and refer to the movement of heat from an areaof higher temperature to an area of cooler temperature. It is intendedthat the movement of heat include any mechanism of heat transmissionknown to one skilled in the art, such as, without limitation,conductive, convective, radiative, etc.

As used herein, the term “emitting” refers to the process of moving heator light from a solid material into the air.

As used herein, “light-emitting surface” refers to a surface of a deviceor object from which light is intentionally emitted. Light may includevisible light and light within the ultraviolet spectrum. An example of alight-emitting surface may include, without limitation, a semiconductorlayer of an LED, or of semiconductor layers to be incorporated into anLED, from which light is emitted.

As used herein, “linear conductive pathway” refers to a conductivepathway that is located along a straight line between two electrodes.

As used herein, “vapor deposited” refers to materials which are formedusing vapor deposition techniques. “Vapor deposition” refers to aprocess of forming or depositing materials on a substrate through thevapor phase. Vapor deposition processes can include any process such as,but not limited to, chemical vapor deposition (CVD) and physical vapordeposition (PVD). A wide variety of variations of each vapor depositionmethod can be performed by those skilled in the art. Examples of vapordeposition methods include hot filament CVD, rf-CVD, laser CVD (LCVD),laser ablation, conformal diamond coating processes, metal-organic CVD(MOCVD), sputtering, thermal evaporation PVD, ionized metal PVD (IMPVD),electron beam PVD (EBPVD), reactive PVD, and the like.

As used herein, “chemical vapor deposition,” or “CVD” refers to anymethod of chemically forming or depositing diamond particles in a vaporform upon a surface. Various CVD techniques are well known in the art.

As used herein, “physical vapor deposition,” or “PVD” refers to anymethod of physically forming or depositing diamond particles in a vaporform upon a surface. Various PVD techniques are well known in the art.

As used herein, “diamond” refers to a crystalline structure of carbonatoms bonded to other carbon atoms in a lattice of tetrahedralcoordination known as sp³ bonding. Specifically, each carbon atom issurrounded by and bonded to four other carbon atoms, each located on thetip of a regular tetrahedron. Further, the bond length between any twocarbon atoms is 1.54 angstroms at ambient temperature conditions, andthe angle between any two bonds is 109 degrees, 28 minutes, and 16seconds although experimental results may vary slightly. The structureand nature of diamond, including its physical and electrical propertiesare well known in the art.

As used herein, “distorted tetrahedral coordination” refers to atetrahedral bonding configuration of carbon atoms that is irregular, orhas deviated from the normal tetrahedron configuration of diamond asdescribed above. Such distortion generally results in lengthening ofsome bonds and shortening of others, as well as the variation of thebond angles between the bonds. Additionally, the distortion of thetetrahedron alters the characteristics and properties of the carbon toeffectively lie between the characteristics of carbon bonded in sp³configuration (i.e. diamond) and carbon bonded in sp² configuration(i.e. graphite). One example of material having carbon atoms bonded indistorted tetrahedral bonding is amorphous diamond.

As used herein, “diamond-like carbon” refers to a carbonaceous materialhaving carbon atoms as the majority element, with a substantial amountof such carbon atoms bonded in distorted tetrahedral coordination.Diamond-like carbon (DLC) can typically be formed by PVD processes,although CVD or other processes could be used such as vapor depositionprocesses. Notably, a variety of other elements can be included in theDLC material as either impurities, or as dopants, including withoutlimitation, hydrogen, sulfur, phosphorous, boron, nitrogen, silicon,tungsten, etc.

As used herein, “amorphous diamond” refers to a type of diamond-likecarbon having carbon atoms as the majority element, with a substantialamount of such carbon atoms bonded in distorted tetrahedralcoordination. In one aspect, the amount of carbon in the amorphousdiamond can be at least about 90%, with at least about 20% of suchcarbon being bonded in distorted tetrahedral coordination. Amorphousdiamond also has a higher atomic density than that of diamond (176atoms/cm³). Further, amorphous diamond and diamond materials contractupon melting.

As used herein, “adynamic” refers to a type of layer which is unable toindependently retain its shape and/or strength. For example, in theabsence of a mold or support layer, an adynamic diamond layer will tendto curl or otherwise deform when the mold or support surface is removed.While a number of reasons may contribute to the adynamic properties of alayer, in one aspect, the reason may be the extreme thinness of thelayer.

As used herein, “growth side,” and “grown surface” may be usedinterchangeably and refer to the surface of a film or layer which isgrows during a CVD process.

As used herein, “substrate” refers to a support surface to which variousmaterials can be joined in forming a semiconductor orsemiconductor-on-diamond device. The substrate may be any shape,thickness, or material, required in order to achieve a specific result,and includes but is not limited to metals, alloys, ceramics, andmixtures thereof. Further, in some aspects, the substrate may be anexisting semiconductor device or wafer, or may be a material which iscapable of being joined to a suitable device.

As used herein, the term “substantially” refers to the complete ornearly complete extent or degree of an action, characteristic, property,state, structure, item, or result. For example, an object that is“substantially” enclosed would mean that the object is either completelyenclosed or nearly completely enclosed. The exact allowable degree ofdeviation from absolute completeness may in some cases depend on thespecific context. However, generally speaking the nearness of completionwill be so as to have the same overall result as if absolute and totalcompletion were obtained. The use of “substantially” is equallyapplicable when used in a negative connotation to refer to the completeor near complete lack of an action, characteristic, property, state,structure, item, or result. For example, a composition that is“substantially free of” particles would either completely lackparticles, or so nearly completely lack particles that the effect wouldbe the same as if it completely lacked particles. In other words, acomposition that is “substantially free of” an ingredient or element maystill actually contain such item as long as there is no measurableeffect thereof.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 1 to about 5” should beinterpreted to include not only the explicitly recited values of about 1to about 5, but also include individual values and sub-ranges within theindicated range. Thus, included in this numerical range are individualvalues such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4,and from 3-5, etc., as well as 1, 2, 3, 4, and 5, individually.

This same principle applies to ranges reciting only one numerical valueas a minimum or a maximum. Furthermore, such an interpretation shouldapply regardless of the breadth of the range or the characteristicsbeing described.

The Invention

The present invention provides semiconductor devices having incorporateddiamond layers and methods of making such devices. Semiconductor devicesare often challenging to cool, particularly those that emit light. Itshould be noted that, even though much of the following description isdevoted to light emitting devices such as LEDs, the scope of the claimsof the present invention should not be limited thereby and that suchteachings are equally applicable to other types of semiconductordevices.

Much of the heat generated by semiconductor devices tends to build upwithin the semiconducting layers, thus affecting the efficiency of thedevice. For example, an LED may consist of a plurality of semiconductorlayers arranged to emit light from a light-emitting surface. As theyhave become increasingly important in electronics and lighting devices,LEDs continue to be developed that have ever increasing powerrequirements. This trend of increasing power has created coolingproblems for such devices. These cooling problems can be exacerbated bythe typically small size of these devices, which may render heat sinkswith traditional aluminum heat fins ineffective due to their bulkynature. Additionally, such traditional heat sinks block the emission oflight if applied to the light-emitting surface of the LED. Because heatsinks cannot interfere with the function of the semiconductor layers orthe light-emitting surface, they are often located at the junctionbetween the LED and a supporting structure such as a circuit board. Sucha heat sink location is relatively remote from the accumulation of muchof the heat, namely, the light-emitting surface and the semiconductorlayers.

It has been discovered that forming a diamond layer within the LEDpackage allows adequate cooling even at high power, while at the sametime maintaining a small LED package size. Additionally, in one aspectthe maximum operating wattage of an LED may be exceeded by drawing heatfrom the semiconductor layers of the LED with a diamond layer in orderto operate the LED at an operating wattage that is higher than themaximum operating wattage for that LED.

Additionally, in both semiconductor devices that emit light and thosethat don't, heat may be trapped within the semiconducting layers due tothe relatively poor thermal conductivity of materials that often make upthese layers. Additionally, crystal lattice mismatches betweensemiconductive layers slow the conduction of heat, thus facilitatingfurther heat buildup. Semiconductor devices have now been developedincorporating layers of diamond that provide, among other things,improved cooling properties to the device. Such layers of diamondincrease the flow of heat laterally through the semiconductor device tothus reduce the amount of heat trapped within the semiconductor layers.This lateral heat transmission may thus effectively improve the thermalproperties of many semiconductor devices. Furthermore, devices accordingto aspects of the present invention have increased lattice matching,thus further improving their thermal cooling properties. Additionally,it should be noted that the beneficial properties provided by diamondlayers may extend beyond cooling, and as such, the present scope shouldnot be limited thereto.

More effective cooling can be achieved within a semiconductor device ifdiamond layers can be incorporated close to the semiconducting layers.One barrier to integration concerns the high dielectric properties ofdiamond materials, particularly those that have substantially singlecrystal lattice configurations. Optimum cooling conditions may beachieved if the diamond layer is within the conductive pathway of thesemiconductor device, however such configurations have been difficult toachieve due to the dielectric properties of diamond. It has now beendiscovered that a conductive diamond layer can function as an electrodeand be coupled to semiconductor layers and thus be within the conductivepathway of the device.

Additionally, by utilizing a conductive diamond layer as an electrode,LED devices can be constructed having a linear conductive pathwaythrough the semiconductive layers between the electrodes. Many prior LEDdevices were constructed such that the conductive pathway from then-type electrode was at a right angle to the conductive pathway from thep-type electrode. Such an “L” shaped conductive pathway caused electronsand holes to be oriented at right angles to one another, thus reducingthe efficiency of the device. The linear conductive pathway according toaspects of the present invention causes electrons and holes to beoriented along the same linear pathway, thus improving the efficiency ofthe LED device.

Accordingly, in one aspect of the present invention, an LED device isprovided. As is shown in FIG. 1, such a device may include a conductivediamond layer 12, a SiC layer or AlN layer 14 coupled to the conductivediamond layer 12, a plurality of semiconductor layers 16, at least oneof which is coupled to the SiC layer or AlN layer 14, and an n-typeelectrode 18 coupled to at least one of the plurality of semiconductorlayers 16. In such a device, the conductive diamond layer 12 functionsas a p-type electrode.

In another aspect of the present invention, as is shown in FIG. 2, asupport substrate 20 may be coupled to the device for convenience inhandling and use. A reflector layer 24 may be formed between theconductive diamond layer 12 and the support substrate 20 to reflectlight back through the conductive diamond layer 12 to improve theefficiency of the LED device. Such a reflective layer may be formed froma variety of reflective materials that are known to those of ordinaryskill in the art. One example of such a reflective material would be alayer of chromium metal or other reflective metal.

FIG. 3 shows selected steps of a method constructing a semiconductorsubstrate that may be used to form an LED device according to particularaspects of the present invention. A single crystal Si growth substrate34 is provided upon which other materials are formed. Although it is notrequired that the Si growth substrate be single crystal, such a singlecrystal lattice configuration may facilitate deposition of additionalmaterials with fewer lattice mismatches as compared to a non-singlecrystal substrate. It may be beneficial to thoroughly clean the Sigrowth substrate to remove any non-crystalline Si or non-Si particlesfrom the wafer prior to deposition that may affect the lattice mismatchbetween the Si growth substrate and the layers formed thereon. Anymethod of cleaning the Si growth substrate would be considered to bewithin the present scope, however, in one aspect the substrate can besoaked in KOH and ultrasonically cleaned with distilled water.

Following cleaning of the Si growth substrate 34, an epitaxial layer ofsingle crystal SiC 32 and an epitaxial diamond layer 36 may be formedthereon, such that the single crystal SiC layer 32 is located betweenthe Si growth substrate 34 and the diamond layer 36. The SiC layer maybe formed separately from the diamond layer, or it may be formed as aresult of, or in conjunction with, the deposition of the diamond layer.For example, the SiC layer may be formed as a result of a gradationprocess from Si to diamond, as is described below. Additionally, the SiClayer may be created in vivo by the deposition of an amorphous diamondlayer onto the Si growth substrate, as is also described below.

Subsequently, a Si layer 38 may be formed on the diamond layer 36. TheSi layer 38 improves the bonding of the Si carrier substrate 42 to thediamond layer 36. The Si carrier substrate 42 has a SiO₂ layer forbonding to the Si layer 38. Following the wafer bonding of the Sicarrier substrate 42 to the Si layer 38, the Si growth substrate 34 maybe removed to expose the SiC layer 32. As has been described, the SiClayer 32 may be used as a growth surface for the deposition ofsemiconductor materials. In one aspect, following formation of the LEDlayers on the SiC layer 32, the Si carrier substrate 42 and the Si layer38 may be removed to expose the conductive diamond layer. A supportsubstrate and/or a reflective layer may then be applied to theconductive diamond layer as is described herein.

In addition to the foregoing, in some embodiments of the invention, AlNmay be substituted for the SiC layer and used between the Si layer andthe diamond layer. In this event, either diamond (i.e. carbon) or Si maybe used to grade to an AlN layer. One example of a gradation techniquethat may be used is Atomic Layer Deposition (ALD). Using such techniquelayers of varying material concentration may be graded (layer gradation)from the starting material to the finish material. For example,beginning with the Si layer, one part of AlN may be codeposited with Si,and then in a subsequent layer, two parts AlN may be included, and soon, until a layer with a substantially even distribution of Si and AlNis produced. Such a gradation produces a super lattice. Such techniquescan further be used to transition from diamond (i.e. carbon) to AlN.Other semiconductor materials, such as GaN can then be added to the AlN.In some aspects, the AlN may be amorphous and serve as a buffer layer toother nitride materials.

Diamond materials have excellent thermal conductivity properties thatmake them ideal for incorporation into semiconductor devices, such asLEDs. The transfer of heat that is present in the semiconductor devicecan thus be accelerated from the device through a diamond material. Itshould be noted that the present invention is not limited as to specifictheories of heat transmission. As such, in one aspect the acceleratedmovement of heat from inside the device can be at least partially due toheat movement into and through a diamond layer. Due to the heatconductive properties of diamond, heat can rapidly spread laterallythrough the diamond layer and to the edges of a semiconductor device.Heat present around the edges will be more rapidly dissipated into theair or into surrounding structures, such as heat spreaders or devicesupports. Additionally, diamond layers having a major portion of surfacearea exposed to air will more rapidly dissipate heat from a device inwhich such a layer is incorporated. Because the thermal conductivity ofdiamond is greater than the thermal conductivity of a semiconductorlayer or other structure to which it is thermally coupled, a heat sinkis established by the diamond layer. As such, heat that builds up in thesemiconductor layer is drawn into the diamond layer and spread laterallyto be discharged from the device. Such accelerated heat transfer mayresult in semiconductor devices with much cooler operationaltemperatures. Additionally, the acceleration of heat transfer not onlycools a semiconductor device, but may also reduce the heat load on manyelectronic components that are spatially located nearby thesemiconductor device.

In some aspects of the present invention, a portion of a diamond layermay be exposed to the air. Such exposure may be limited to the edges ofthe layer in some cases, or it may be a larger proportion of surfacearea, such as would be the case for a diamond layer having one sideexposed. In such aspects, the accelerated movement of heat away from asemiconductor layer may be at least partially due to heat movement fromthe diamond layer to air. For example, a diamond material such asdiamond-like carbon (DLC) has exceptional heat emissivitycharacteristics even at temperatures below 100° C., and as such, mayeffectively radiate heat directly to the air. Many semiconductormaterials that comprise a device conduct heat much better than they emitheat. As such, heat can be conducted through a semiconductor material toa DLC layer, spread laterally through the DLC layer, and subsequentlyemitted to the air along the edges or other exposed surfaces. Due to thehigh heat conductive and radiative properties of DLC, heat movement fromthe DLC layer to air can be greater than heat movement from thesemiconductor layer to air. Also, heat movement from the semiconductordevice to the DLC layer can be greater than heat movement from thesemiconductor device to the air. As such, the layer of DLC can serve toaccelerate heat transfer away from the semiconductor layer more rapidlythan heat can be transferred through the semiconductor device itself, orfrom the semiconductor device to the air.

As has been suggested, various diamond materials may be utilized toprovide accelerated heat transferring properties to a semiconductordevice. Non-limiting examples of such diamond materials may includediamond, DLC, amorphous diamond, and combinations thereof. It should benoted, however, that any form of natural or synthetic diamond materialthat may be utilized to cool a semiconductor device is considered to bewithin the present scope.

It should be understood that the following is a very general discussionof diamond deposition techniques that may or may not apply to aparticular diamond layer or application, and that such techniques mayvary widely between the various aspects of the present invention.Generally, diamond layers may be formed by any means known, includingvarious vapor deposition techniques. Any number of known vapordeposition techniques may be used to form these diamond layers. The mostcommon vapor deposition techniques include chemical vapor deposition(CVD) and physical vapor deposition (PVD), although any similar methodcan be used if similar properties and results are obtained. In oneaspect, CVD techniques such as hot filament, microwave plasma,oxyacetylene flame, rf-CVD, laser CVD (LCVD), metal-organic CVD (MOCVD),laser ablation, conformal diamond coating processes, and direct currentarc techniques may be utilized. Typical CVD techniques use gas reactantsto deposit the diamond or diamond-like material in a layer, or film.These gases generally include a small amount (i.e. less than about 5%)of a carbonaceous material, such as methane, diluted in hydrogen. Avariety of specific CVD processes, including equipment and conditions,as well as those used for boron nitride layers, are well known to thoseskilled in the art. In another aspect, PVD techniques such assputtering, cathodic arc, and thermal evaporation may be utilized.Further, specific deposition conditions may be used in order to adjustthe exact type of material to be deposited, whether DLC, amorphousdiamond, or pure diamond. It should also be noted that manysemiconductor devices such as LEDs may be degraded by high temperature.Care may need to be taken to avoid damage during diamond deposition byforming at lower temperatures. For example, if the semiconductorcontains InN, deposition temperatures of up to about 600° C. may beused. In the case of GaN, layers may be thermally stable up to about1000° C. Additionally, preformed layers can be brazed, glued, orotherwise affixed to the semiconductor layer or to a support substrateof the semiconductor device using methods which do not unduly interferewith the heat transference of the diamond layer or the functionality ofthe device.

An optional nucleation enhancing layer can be formed on the growthsurface of a substrate in order to improve the quality and depositiontime of a diamond layer. Specifically, a diamond layer can be formed bydepositing applicable nuclei, such as diamond nuclei, on a diamondgrowth surface of a substrate and then growing the nuclei into a film orlayer using a vapor deposition technique. In one aspect of the presentinvention, a thin nucleation enhancer layer can be coated upon thesubstrate to enhance the growth of the diamond layer. Diamond nuclei arethen placed upon the nucleation enhancer layer, and the growth of thediamond layer proceeds via CVD.

A variety of suitable materials will be recognized by those in skilledin the art which can serve as a nucleation enhancer. In one aspect ofthe present invention, the nucleation enhancer may be a materialselected from the group consisting of metals, metal alloys, metalcompounds, carbides, carbide formers, and mixtures thereof. Examples ofcarbide forming materials may include, without limitation, tungsten (W),tantalum (Ta), titanium (Ti), zirconium (Zr), chromium (Cr), molybdenum(Mo), silicon (Si), and manganese (Mn). Additionally, examples ofcarbides include tungsten carbide (WC), silicon carbide (SiC), titaniumcarbide (TiC), zirconium carbide (ZrC), and mixtures thereof amongothers.

The nucleation enhancer layer, when used, is a layer which is thinenough that it does not to adversely affect the thermal transmissionproperties of the diamond layer. In one aspect, the thickness of thenucleation enhancer layer may be less than about 0.1 micrometers. Inanother aspect, the thickness may be less than about 10 nanometers. Inyet another aspect, the thickness of the nucleation enhancer layer isless than about 5 nanometers. In a further aspect of the invention, thethickness of the nucleation enhancer layer is less than about 3nanometers.

Various methods may be employed to increase the quality of the diamondin the nucleation surface of the diamond layer which is created by vapordeposition techniques. For example, diamond particle quality can beincreased by reducing the methane flow rate, and increasing the totalgas pressure during the early phase of diamond deposition. Suchmeasures, decrease the decomposition rate of carbon, and increase theconcentration of hydrogen atoms. Thus a significantly higher percentageof the carbon will be deposited in a sp³ bonding configuration, and thequality of the diamond nuclei formed is increased. Additionally, thenucleation rate of diamond particles deposited on the growth surface ofthe substrate or the nucleation enhancer layer may be increased in orderto reduce the amount of interstitial space between diamond particles.Examples of ways to increase nucleation rates include, but are notlimited to; applying a negative bias in an appropriate amount, oftenabout 100 volts, to the growth surface; polishing the growth surfacewith a fine diamond paste or powder, which may partially remain on thegrowth surface; and controlling the composition of the growth surfacesuch as by ion implantation of C, Si, Cr, Mn, Ti, V, Zr, W, Mo, Ta, andthe like by PVD or PECVD. PVD processes are typically at lowertemperatures than CVD processes and in some cases can be below about200° C. such as about 150° C. Other methods of increasing diamondnucleation will be readily apparent to those skilled in the art.

In one aspect of the present invention, the diamond layer may be formedas a conformal diamond layer. Conformal diamond coating processes canprovide a number of advantages over conventional diamond film processes.Conformal diamond coating can be performed on a wide variety ofsubstrates, including non-planar substrates. A growth surface can bepretreated under diamond growth conditions in the absence of a bias toform a carbon film. The diamond growth conditions can be conditions thatare conventional CVD deposition conditions for diamond without anapplied bias. As a result, a thin carbon film can be formed which istypically less than about 100 angstroms. The pretreatment step can beperformed at almost any growth temperature such as from about 200° C. toabout 900° C., although lower temperatures below about 500° C. may bepreferred. Without being bound to any particular theory, the thin carbonfilm appears to form within a short time, e.g., less than one hour, andis a hydrogen terminated amorphous carbon.

Following formation of the thin carbon film, the growth surface may thenbe subjected to diamond growth conditions to form a conformal diamondlayer. The diamond growth conditions may be those conditions which arecommonly used in traditional CVD diamond growth. However, unlikeconventional diamond film growth, the diamond film produced using theabove pretreatment steps results in a conformal diamond film thattypically begins growth substantially over the entire growth surfacewith substantially no incubation time. In addition, a continuous film,e.g. substantially no grain boundaries, can develop within about 80 nmof growth. Diamond layers having substantially no grain boundaries maymove heat more efficiently than those layers having grain boundaries.

Various techniques may be employed to render a diamond layer conductive.Such techniques are known to those of ordinary skill in the art. Forexample, various impurities may be doped into the crystal lattice of thediamond layer. Such impurities may include elements such as Si, B, P, N,Li, Al, Ga, etc. In one specific aspect, for example, the diamond layermay be doped with B. Impurities may also include metallic particleswithin the crystal lattice, provided they do not interfere with thefunction of the device, such as by blocking light emitted from an LED.

For some diamond layers, particularly those on which semiconductorlayers are to be formed, it may be beneficial to create a growthsubstrate upon which the semiconductor material can be formed withminimal crystal lattice dislocations as a substantially single crystal.Minimizing crystal lattice dislocations may be facilitated by utilizinga growth substrate that is substantially a single crystal and hasproperties such that strong bonding interactions with the semiconductormaterial may be achieved. In one aspect, such a substrate includes asubstantially single crystal diamond layer having a substantially singlecrystal SiC layer epitaxially coupled thereto. The substantially singlecrystal nature of the SiC layer facilitates the deposition of asemiconductor such as GaN or AlN as a substantially single crystal.Additionally, the epitaxial relationship from the diamond layer throughthe SiC layer and to the semiconductor layer increases thermalconduction to the diamond layer, thus improving the cooling propertiesof the device.

Various methods are possible for building such a diamond/SiC compositesubstrate. Any such method would be considered to be within the scope ofthe present invention. For example, in one aspect such a substrate maybe created by grading a single crystal Si wafer into a single crystaldiamond layer. In other words, the Si wafer would gradually transitionfrom Si to SiC and then to diamond. Techniques for such grading arefurther discussed in the Applicant's copending U.S. patent applicationSer. No. 11/809,806 which is incorporated herein by reference. Othermethods of growing one material on another or otherwise attaching twomaterials together are also found in Applicant's copending U.S. patentapplication Ser. Nos. 11/809,718; 11/809,721; 61/187,557; 61/230,055;and 61/259,948, each of which are incorporated herein by reference. Inaddition to the above described benefits of minimizing crystaldislocations, substantially single crystal diamond layers aresubstantially transparent to light and are thus useful in constructinglight-emitting semiconductor devices such as LEDs and laser diodes.

Following thickening of the diamond layer or attachment of a supportsubstrate to the diamond layer, the Si wafer may be removed by anymethod know to one of ordinary skill in the art. The resulting structureincludes a substantially single crystal diamond layer having asubstantially single crystal SiC layer epitaxially coupled thereto. Asemiconductor material may then be epitaxially formed on the SiC layerby any method know to one of ordinary skill in the art. In one aspectsuch deposition may occur in a graded manner similar to the techniquesused in forming the diamond layer on the Si wafer.

The diamond layers according to aspects of the present invention may beof any thickness that would allow thermal cooling of a semiconductordevice. Thicknesses may vary depending on the application and thesemiconductor device configuration. For example, greater coolingrequirements may require thicker diamond layers. The thickness may alsovary depending on the material used in the diamond layer. That beingsaid, in one aspect a diamond layer may be from about 10 to about 50microns thick. In another example, a diamond layer may be less than orequal to about 10 microns thick. In yet another example, a diamond layermay be from about 50 microns to about 100 microns thick. In a furtherexample, a diamond layer may be greater than about 50 microns thick. Inyet a further example, a diamond layer may be an adynamic diamond layer.

SiC layers according to aspects of the present invention may have avariety of thicknesses, depending on the method of deposition of the SiClayer and the intended uses of the device. In some aspects the SiC layermay be merely thick enough to orient the crystal lattice of the layersbeing formed thereon. In other aspects, thicker SiC layers may bebeneficial. With such variation in mind, in one aspect the SiC layer maybe less than or equal to about 1 micron thick. In another aspect, theSiC layer may be less than or equal to about 500 nanometers thick. Inyet another aspect, the SiC layer may be less than or equal to about 1nanometer thick. In a further aspect, the SiC layer may be greater thanabout 1 micron thick.

As has been described, the semiconductor devices according to aspects ofthe present invention include a plurality of semiconductor layersassociated with one or more diamond layers. These semiconductor layersmay be associated with a diamond layer by a variety of methods known toone of ordinary skill in the art. In one aspect of the presentinvention, however, one or more semiconductor layers may be formed on adiamond layer, or as is described above, on a SiC layer coupled to adiamond layer.

A semiconductor layer may be formed on a substrate such as a SiC layerusing a variety of techniques known to those of ordinary skill in theart. One example of such a technique is a MOCVD process.

The semiconductor layer may include any material that is suitable forforming electronic devices, semiconductor devices, or the like. Manysemiconductors are based on silicon, gallium, indium, and germanium.However, suitable materials for the semiconductor layer can include,without limitation, silicon, silicon carbide, silicon germanium, galliumarsenide, gallium nitride, germanium, zinc sulfide, gallium phosphide,gallium antimonide, gallium indium arsenide phosphide, aluminumphosphide, aluminum arsenide, aluminum gallium arsenide, galliumnitride, boron nitride, aluminum nitride, indium arsenide, indiumphosphide, indium antimonide, indium nitride, and composites thereof. Inone aspect, however, the semiconductor layer can include silicon,silicon carbide, gallium arsenide, gallium nitride, gallium phosphide,aluminum nitride, indium nitride, indium gallium nitride, aluminumgallium nitride, or composites of these materials.

In some additional embodiments, non-silicon based devices can be formedsuch as those based on gallium arsenide, gallium nitride, germanium,boron nitride, aluminum nitride, indium-based materials, and compositesthereof. In another embodiment, the semiconductor layer can comprisegallium nitride, indium gallium nitride, indium nitride, andcombinations thereof. In one specific aspect, the semiconductor materialis gallium nitride. In another specific aspect, the semiconductormaterial is aluminum nitride. Other semiconductor materials which can beused include Al₂O₃, BeO, W, Mo, c-Y₂O₃, c-(Y_(0.9)La_(0.1))₂O₃,c-Al₂₃O₂₇N₅, c-MgAl₂O₄, t-MgF₂, graphite, and mixtures thereof. Itshould be understood that the semiconductor layer may include anysemiconductor material known, and should not be limited to thosematerials described herein. Additionally, semiconductor materials may beof any structural configuration known, for example, without limitation,cubic (zincblende or sphalerite), wurtzitic, rhombohedral, graphitic,turbostratic, pyrolytic, hexagonal, amorphous, or combinations thereof.As has been described, the semiconductor layer 14 may be formed by anymethod known to one of ordinary skill in the art. Various known methodsof vapor deposition can be utilized to deposit such layers and thatallow deposition to occur in a graded manner. Additionally, surfaceprocessing may be performed between any of the deposition stepsdescribed in order to provide a smooth surface for subsequentdeposition. Such processing may be accomplished by any means known, suchas by chemical etching, polishing, buffing, grinding, etc.

In one aspect of the present invention, at least one of thesemiconductor layers may be gallium nitride (GaN). GaN semiconductorlayers may be useful in constructing LEDs and other semiconductordevices. In some cases it may be beneficial to gradually transitionbetween the SiC or other substrate and the semiconductor layer. Forexample, gradually transitioning an indium nitride (InN) semiconductorsubstrate into a GaN semiconductor layer may occur by fixing theconcentration of the N being vapor deposited and varying the depositedconcentration of Ga and of In such that a ratio of Ga:In graduallytransitions from about 0:1 to about 1:0. In other words, the sources ofGa and In are varied such that as the In concentration is decreased, theGa concentration is increased. The gradual transition functions togreatly reduce the lattice mismatch observed when forming GaN directlyon InN.

In another aspect, at least one of the semiconductor layers may be alayer of aluminum nitride (AlN). The AlN layer may be deposited on asubstrate by any means known to one of ordinary skill in the art. Aswith the GaN layer described above, gradually transitioning betweensemiconductor layers may improve the functionality of the semiconductordevice. For example, in one aspect AlN may be formed on a semiconductorsubstrate of InN by gradually transitioning the layer of InN into thelayer of AlN. Such a gradual transition may include, for example,gradually transitioning the layer of InN into the layer of AlN by fixingthe concentration of N being deposited and varying the depositedconcentration of In and of Al such that a ratio of In:Al graduallytransitions from about 0:1 to about 1:0. Such a gradual transition maygreatly reduce the lattice mismatch observed when forming AlN on InNdirectly. Surface processing may be performed between any of thedeposition steps described in order to provide a smooth surface forsubsequent deposition. Such processing may be accomplished by any meansknown, such as by chemical etching, polishing, buffing, grinding, etc.

As has been described, an n-type electrode is incorporated into an LEDdevice as an electrical contact for the semiconductive layers. N-typeelectrodes, including their use and formation, are well known to thoseof ordinary skill in the art, and will not be discussed in detailherein.

Examples

The following examples illustrate various techniques of making asemiconductor device such as an LED according to aspects of the presentinvention. However, it is to be understood that the following are onlyexemplary or illustrative of the application of the principles of thepresent invention. Numerous modifications and alternative compositions,methods, and systems can be devised by those skilled in the art withoutdeparting from the spirit and scope of the present invention. Theappended claims are intended to cover such modifications andarrangements. Thus, while the present invention has been described abovewith particularity, the following Examples provide further detail inconnection with several specific embodiments of the invention.

Example 1

A semiconductor substrate may be formed as follows:

A single crystal Si wafer is obtained and cleaned by soaking in KOH andultrasound cleaning with distilled water to remove any non-crystallineSi and foreign debris. A conformal amorphous carbon coating is appliedto the cleaned surface of the Si wafer by exposing the wafer to CVDdeposition conditions without an applied bias. Following carbonizationof the surface, amorphous diamond is deposited for approximately 30minutes at 800° in 1% CH₄ and 99% H₂. The amorphous carbon coating isthen removed with H₂ or F₂ treatment for about 60 minutes, at 900°.Removal of the amorphous carbon coating exposes an epitaxial SiC layerthat has formed in situ between the Si wafer and the amorphous carboncoating. The thickness of the SiC layer is approximately 10 nm.

A transparent diamond coating 10 microns thick is then deposited ontothe SiC layer by CVD deposition of CH₄ for approximately 10 hours. After10 hours, the CH₄ source is then switched to SiH₄ for approximately 10minutes to deposit a 1 micron thick Si layer.

A Si carrier substrate having a SiO₂ surface is wafer bonded to the 1micron thick Si layer at the SiO₂ surface. Following wafer bonding, thesingle crystal Si wafer is removed to expose the SiC layer by etchingwith HF+3HNO₂+H₂O. Further details regarding etching Si materials may befound in U.S. Pat. No. 4,981,818, which is incorporated herein byreference.

Example 2

An LED device may be constructed as follows:

A semiconductor substrate is obtained as in Example 1. GaN semiconductorlayers are deposited onto the exposed SiC layer by MOCVD with GaH₃ andNH₃ source materials.

Of course, it is to be understood that the above-described arrangementsare only illustrative of the application of the principles of thepresent invention. Numerous modifications and alternative arrangementsmay be devised by those skilled in the art without departing from thespirit and scope of the present invention and the appended claims areintended to cover such modifications and arrangements. Thus, while thepresent invention has been described above with particularity and detailin connection with what is presently deemed to be the most practical andpreferred embodiments of the invention, it will be apparent to those ofordinary skill in the art that numerous modifications, including, butnot limited to, variations in size, materials, shape, form, function andmanner of operation, assembly and use may be made without departing fromthe principles and concepts set forth herein.

What is claimed is:
 1. A method of making an LED device, comprising:forming epitaxially a SiC or AlN layer on a substantially single crystalSi wafer; forming epitaxially a substantially single crystal diamondlayer on the SiC or AlN layer; doping the diamond layer to form aconductive diamond layer; removing the Si wafer to expose the SiC or AlNlayer opposite to the diamond layer; forming epitaxially a plurality ofsemiconductor layers on the SiC or AlN layer such that at least one ofthe semiconductive layers contacts the SiC or AlN layer; and coupling ann-type electrode to at least one of the semiconductor layers, such thatthe plurality of semiconductor layers is functionally located betweenthe conductive diamond layer and the n-type electrode, and where theconductive diamond layer and the n-type electrode are arranged such thatthere is a substantially linear conductive pathway therebetween.
 2. Themethod of claim 1, wherein forming an epitaxial layer of a substantiallysingle crystal diamond layer further includes compositionally grading asurface of the Si wafer from Si to SiC or AlN to form the SiC or AlNlayer, and compositionally grading a surface of the SiC or AlN layer todiamond to form the diamond layer.
 3. The method of claim 2, whereinforming an epitaxial layer of SiC further includes: forming a conformalamorphous diamond layer on the Si growth substrate to form the SiC layerin situ therebetween; and removing the conformal amorphous diamond layerto expose the SiC layer.
 4. The method of claim 3, further comprisingforming the conductive diamond layer on the exposed SiC layer.
 5. Themethod of claim 1, further comprising: forming a Si layer on the diamondlayer on a surface opposite the SiC or AlN layer prior to removing theSi wafer; and bonding a Si carrier substrate having a SiO₂ layer to theSi layer, such that the Si layer is bonded to the SiO₂ layer.